The present invention relates to a tool driving unit, and more particularly to a single-shaft tool driving unit for moving a tool such as a tap or a drill in axial direction while rotating the same.
Heretofore, tool driving units such as tapping units have at least two shafts, i.e., the shaft of a straight drive device coupled to a motor shaft for moving a tool back and forth and the shaft of a rotary drive device coupled to another motor shaft for rotating the tool. The back-and-forth movement and the rotary movement are transmitted from the two shafts to a spindle supporting the tool through gear trains.
There has been proposed a tool driving unit in which a single motor is disposed coaxially with a spindle having a ball screw shaft portion and a ball spline shaft portion, for selectively rotating and moving back and forth the spindle (see Japanese Laid-Open Patent Publication No. 61-38892).
According to the former tool driving unit, the devices for generating the back-and-forth movement and the rotary movement are composed of the two or more shafts that are not positioned coaxially. Therefore the tool driving unit has a large outside diameter, and requires a large installation space. The two shafts have to be positioned with increased accuracy when the tool driving unit is installed in place. Another problem is that the tool driving unit is made up of a large number of parts and hence complex in structure.
The latter tool driving unit is disadvantageous in that since the spindle can selectively be rotated and moved back and forth by the clutch mechanism, the tool cannot be moved back and forth while it is being rotated.